Centrifugal pumps—as one example of many kinds of rotating machines for which the invention may be used—are normally mechanically driven through induced magnetism created by a motor stator. In such pumps, a magnetic field interacts with a magnet included as part of a rotor mechanically attached to a shaft so as to rotate/drive the rotor assembly about the shaft. As the magnetic field causes the rotor to rotate, an attached impeller is also caused to rotate, which produces the pumping action of the pump. The pumping action, along with the magnetic forces through the stator and rotor produce both radial and axial forces that must be counter-balanced. Normally, in a wet rotor pump design (i.e. with the fluid being pumped in contact with the rotor), the forces are balanced by separate thrust and radial bearings, or some combination thereof, either attached to or acting on the rotor/shaft. The bearings serve to absorb forces and align the rotor about a centerline.
For high speed pumps (above about 12,000 RPM), normal bearing systems—such as those including ball bearings or carbon/ceramic bearing faces—tend not to last.
It would be advantageous to be able to provide a shaft that includes as an integral component—i.e. as a portion of the shaft—the bearings needed to counterbalance the radial and axial forces caused by driving the pump and caused by the pumping action. Such a shaft would have to be made of a material suitable for a bearing surface, which in case of high-speed applications is especially demanding.
U.S. Pat. No. 4,120,618 to Klaus describes a magnetic drive pump (as opposed to a wet rotor pump), with the magnetic drive pump having a shaft made out of a synthetic plastic, but the shaft synthetic plastic is apparently not of a material able to serve as a bearing surface, and so graphite and/or molybdenum disulfide or some other bearing material is imbedded in the shaft (only) at the locations where the shaft is to provide a bearing surface. Further, the plastic shaft described there interfaces with plastic material (the gap tube 7) of the pump described there, whereas it may be advantageous to have bearing surfaces on the shaft interface with a metallic bearing carrier (on the stator).
U.S. Pat. No. 5,769,618 discloses a flexible shaft having a rod-like member made from PEEK (poly-ether-ether-ketone). It is not a shaft about which a rotor rotates, but instead serves to couple a drive shaft to an external thread type rotor; the drive shaft is rotatably supported by ball bearings of a bearing unit. A metal rod is provided in the middle of the flexible shaft in a longitudinal direction, or a metal sleeve is mounted over the outer surface of the flexible shaft. The flexible shaft does not have on it a bearing surface.
U.S. Pat. No. 5,131,818 describes the use of PEEK material as a cylinder bushing in a reciprocating piston pump. There is no teaching or description of the use of PEEK material for making a shaft, let alone a shaft having a bearing surface.
U.S. Pat. No. 5,873,697 describes using PEEK material as a centrifugal pump wear ring for helping to control impeller wear ring clearances. There is no teaching or suggestion of using PEEK material for making a shaft having a bearing surface.
U.S. Pat. No. 4,047,847 teaches the use of a ceramic shaft, not a shaft made of engineering plastic, and teaches the use of a rotor formed of synthetic resin. There is no teaching or suggestion of using engineering plastic such as PEEK in making a shaft having a bearing surface.
Thus, despite prior art teaching making a shaft, what is still needed is a shaft that includes a bearing surface as an integral component, thereby providing a rotating machine having fewer separate components and so potentially reducing manufacturing/assembly costs and improving reliability.